1. Technical Field
This invention relates in general to a magnetoresistive read sensor for reading signals recorded in a magnetic medium and, more particularly, this invention relates to an improved orthogonal magnetoresistive read sensor with a series flux guide.
2. Description of the Background Art
A magnetoresistive (MR) read sensor (head) has been shown to be capable of reading data from a magnetic surface of a magnetic disk at great linear densities. An MR sensor detects magnetic fields through the resistance changes of its MR sensing element (also referred to as "MR layer" and/or "MR material") as a function of the strength and direction of the magnetic flux being sensed by the MR sensing element. MR read sensors are of great interest for several reasons: MR sensors' intrinsic noise is lower than inductive sensors' intrinsic noise, thus providing improved signal-to-noise (S/N) performance; MR sensors sense magnetic flux (.phi.) as compared to inductive heads which sense the time rate of flux change, d.phi./dt, thus making the reproduction of the signal recorded on a medium independent of the relative velocity between the MR sensor and the medium; and MR sensors have bandwidth in the gigahertz (gHz) range which allows area storage density well in excess of one gigabit per square inch.
MR sensors currently being used or under development fall into two broad categories: 1) anisotropic magnetoresistive (AMR) sensors and 2) giant magnetoresistive (GMR) sensors. In the AMR sensors, the resistance of the MR layer varies as the function of cos.sup.2 .alpha. where .alpha. is the angle between the magnetization and the direction of the sense current flowing in the MR layer. The MR layer is made of ferromagnetic material. U.S. Pat. No. 5,018,037 entitled "Magnetoresistive Read Transducer Having Hard Magnetic Bias", granted to Krounbi et al. on May 21, 1991, discloses an MR sensor operating on the basis of the AMR effect.
In the GMR sensor, the resistance of the MR sensing element varies as a function of the spin-dependent transmission of the conduction electrons between the magnetic layers separated by a non-magnetic layer and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. The magnetic layers are made of ferromagnetic material. GMR sensors using only two layers of ferromagnetic material separated by a layer of non-magnetic metallic material are generally referred to as spin valve (SV) MR sensors. A GMR sensor fabricated from the appropriate materials provides improved sensitivity and greater change in resistance than observed in sensors using the AMR effect. U.S. Pat. No. 5,206,590 entitled "Magnetoresistive Sensor Based On The Spin Valve Effect", granted to Dieny et al. on Apr. 27, 1993, discloses an MR sensor operating on the basis of the spin valve effect.
MR sensors further fall into two configurations. In one configurations the sense current is conducted in the MR sensing element parallel to the air bearing surface. Air bearing surface (ABS) refers to the surface of the slider adjacent the magnetic disk surface. In the other configurations the sense current is conducted in the MR sensing element perpendicular to the air bearing surface. The former configuration is referred to as conventional MR read sensors and the latter configuration is known as orthogonal MR read sensors.
A perspective view of an orthogonal MR sensor 10 having a read surface 12 above a circular track 30 on a storage medium is shown in FIG. 1 Read surface 12 forms a part of the air bearing surface 20 FIGS. 2A and 2B also show a front view and an ABS view (the MR sensor as seen from the air bearing surface),.sub.1 respectively, of an orthogonal MR sensor 10 MR sensor 10 comprises MR sensing element 50 formed on a suitable substrate 60, biasing end regions 52 and 54 formed on substrate 60, bottom lead 56, and top lead 58. Each biasing end region forms a contiguous junction with sensing element 50. Bottom lead 56 is further in contact with the bottom portion of MR sensing element 50 and top lead 58 is connected to the top portion of sensing element 50. Width 22 of MR sensing element 50 is defined as the track width of the MR sensor. MR sensing element 50 has an easy axis which extends parallel to ABS 20.
The orthogonal MR sensor, as shown in FIG. 2A, has several advantages, namely: the amplitude of its read back signal can be made substantially independent of its track width 22 and the bottom portion of the MR sensor at the ABS can be electrically grounded together with the shields, thus eliminating problems arising from electrical shorts between the sensing element and the shields. However, the orthogonal MR sensor also has several disadvantages, namely: (1) it has a very poor read back sensitivity. This is due to the fact that sensing element sensitivity is seriously affected among other things, by the height of the bottom lead which is in contact with the MR sensing element and shunts current away from the sensing element. For example, if the height of a sensing element is about 1.0 micron with about .+-.0.5 micron variation in the height due to the statistical variations present in its manufacturing process and if the height of the bottom lead is about 0.4 micron with about .+-.0.2 micron variation in the height of the bottom lead, then in some of the sensors produced with this manufacturing process, virtually all the sensing current is shunted by the bottom lead severely degrading the sensed signal amplitude; (2) MR sensors, especially spin valve MR sensors, typically utilize materials such as copper (Cu), cobalt (Co) or nickel iron (NiFe) in order to form the layers of the sensing element. The presence of these materials at the head/disk interface can cause head failure due to head corrosion; (3) in near contact recording applications, the presence of the MR sensing element of an MR sensor at the head/disk interface can cause sensor failure due to mechanical and/or thermal phenomena; and, (4) it is critical to accurately control the size of the sensing element during the lapping process since the performance of MR sensors are dependent on the stripe height of their sensing element. However, mechanical lapping processes currently used to lap MR sensors have substantial manufacturing tolerances associated with them. As a result, it is extremely difficult to accurately control the stripe height of the MR sensors during the lapping process. This results in producing MR sensors with unpredictable sensing efficiency for sensing read back signals.
Therefore, there is a need for an invention which teaches how to substantially eliminate the aforementioned problems and at the same time improve the sensitivity and corrosion resistant of orthogonal MR sensors.